One known method for exposuring photographic materials is an image forming method using a scanner system wherein the original is scanned, and a silver halide photographic material is exposed to light on the basis of the resulting image signals to form a negative image or a positive image corresponding to the image of the original. The scanner system has been widely used in the field of printing plate making in recent years.
There are many recording devices which utilize the image forming method using a scanner system. Among them, a dot generator system using a dot generator is widely used at present.
Conventional light sources for recording with these scanner system recording devices include a glow lamp, a xenon lamp, a mercury vapor lamp, a tungsten lamp and a light-emitting diode.
However, these light sources have practical disadvantages in that their outputs are low and their life is short. Scanners have been developed using, as a light source for the scanner system, a coherent laser beam source such as a He--Ne laser, an argon laser, a He--Cd laser or a semiconductor laser.
Various characteristics are required for light sensitive materials used in these scanner systems. Particularly, exposure is carried out in a short time of 1.times.10.sup.-3 to 1.times.10.sup.-8 seconds. Hence, the light-sensitive materials must be high-sensitivity and high-contrast under the above conditions. Further, high-sensitivity light-sensitive materials may advantageously throttle output, so that the life of the laser tube can be prolonged. Furthermore, it is necessary that laser beam be regulated, for example, by using slits to obtain good dots. High-sensitivity light-sensitive materials are required to cope with a reduction in laser output caused by the regulation of laser beam. Particularly, many scanners using argon laser as a light source are used for the purposes of obtaining a high output and of narrowly regulated laser beam.
Generally, light-sensitive materials for an argon laser are processed by a technique called spectral sensitization with sensitizing dyes. These dyes have an absorption at about 488 nm to impart sensitivity to a light having a wavelength of 488 nm which is a wavelength of the argon laser beam. However, light-sensitive materials after processing have a residual color caused by the sensitizing dyes, and the commercial value of the finished products is often lowered. Sometimes intrinsic desensitization is caused by the amounts of the sensitizing dyes added. Examples of methods for increasing the efficiency of spectral sensitization include those described in JP-B-49-25500 (the term "JP-B" as used herein means an "examined Japanese patent publication") for a He--Ne laser beam and those described in JP-A-59-19032 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-59-192242 for a semiconductor laser beam. However, sometimes there are problems of residual color and deterioration of UV transmission in dot to dot work stage after exposure.
Silver halide emulsions exposed under high intensity over a short period of time have the disadvantage that development proceeds slowly and sensitivity greatly fluctuates when the compositions of the developing solutions are changed and when development temperature or time is changed.
There has been a demand to promote operation and to speed up work in the printing industry in recent years. Therefore, there is a need to speed up scanning and shorten the processing time of the light-sensitive materials.
To meet the above needs in the printing industry, there is a demand to speed up scanning in exposure devices (e.g., scanner, plotter) and to increase screen ruling or stop down beams to improve the quality of the image. With silver halide photographic materials, it is demanded to provide light-sensitive materials which have high sensitivity, are excellent in stability, and allow rapid processing or rapid development to be conducted.
The terms "rapid processing" and "rapid development" as used herein refer to processing which takes 15 to 60 seconds from the time that the top of the film is introduced into the automatic processor and then passed through a development bath, a transfer zone, a fixing bath, a transfer zone, a rinsing bath and the drying zone, until the top of the film leaves the drying zone.
Many patent specifications disclose that sensitivity can be enhanced when chemical sensitization is carried out with selenium compounds. Examples of such selenium compounds are disclosed in JP-B-44-15748 and JP-B-43-13489. Further, JP-B-43-22090 discloses that sensitivity can be increased under high intensity by the use of water-soluble iridium compounds. Sensitivity can be certainly increased by these methods.
However, when developing solutions are used for processing light-sensitive materials, the developing solutions are oxidized by oxygen in air and are easily exhausted. Hence it is very difficult to keep the same composition as that of a fresh developing solution. It is desirable that a difference in sensitivity between the processing of a fresh developing solution and the processing of an exhausted solution be as small as possible. The development time is inevitably shortened in rapid processing, in particular. Hence, dependence of processing on the compositions of the developing solutions is high, and there is a demand to improve the constitution of the light-sensitive materials.